The structure and function of the renal lymphatic system in health and disease is under investigation. Physiologic experiments involve the collection of renal hilar (Hl) and capsular (CL) lymph, thoracic duct lymph (TDL), renal venous (RVP) and arterial plasma (AP) and urine, in anaesthetized dogs. Concomitant histological studies with light and electron microscopy are also in progress. Under control conditions Na ion and Cl concentrations in HL are significantly higher than those in the other L or P samples. Conversely glucose concentrations in HL are less than those in P or TDL which in turn are significantly less than those in CL. L to P concentration differences disappear during experimental hydronephrosis maintained for from 1 to 3 weeks. Conclusions from experiments to date include 1) both HL and CL derive a component from tubular reabsorbate, 2) HL drains in part the outer medulla, 3) CL drains the superficial cortex, 4) in chronic hydronephrosis there is a major diversion of lymph from HL to CL, 5) this increase in CL flow is not due to simple diversion of urine to lymph. Current and projected studies include a comparison of the renal lympatic system in water and saline diuresis, and a detailed histological study of the intrarenal lymphatic distribution. BIBLIOGRAPHIC REFERENCES: O'Morchoe, C.C.C. The function of renal lymph. Proc. Vth. Int. Cong. Lymph. 197-98, 1975. O'Morchoe, C.C.C., O'Morchoe, P.J. and Donati, E.J. Comparison of hilar and capsular renal lymph. Am. J. Physiol. 229(2), 416-421, 1975.